I believe the W124 series is similar to the W123 and W201 series in that the areas around the hood hinges have a drain. If you live in an area with squirrels and other rodents that live outside, you may find this area full of acorns and leaves, or if you park under trees of any kind, you may find it clogged with similar debris. So, to get started, you may want to remove the visible junk in the area.
I regularly clean and spray my battery support area with penetrating fluid or other spray oil to keep any corrosion down. I use a mat under the battery (I got mine from Griot's Garage) to neutralize any acid from the battery that might get there, before it damages the tray.
Good luck, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)